Over
the past two decades, ice loss from the Greenland Ice Sheet increased four-fold
contributing to one-quarter of global sea level rise. However, the chain of
events and physical processes that contributed to it has remained elusive. One
likely trigger for the speed up and retreat of glaciers that contributed to
this ice loss is ocean warming.

ADVERTISEMENT

A
review paper by physical oceanographers Fiamma Straneo at Woods Hole
Oceanographic Institution (WHOI) and Patrick Heimbach at MIT published in
Nature explains what scientists have learned from their research on and around
Greenland over the past 20 years and describes the measurements and technology
needed to continue to move the science forward.

The
Greenland Ice Sheet is a 1.7 million-square-kilometer, 2-mile thick layer of
ice that covers Greenland. At its edge, glaciers that drain the ice sheet
plunge into coastal fjords that are over 600 meters deep — thus exposing the
ice sheet edges to contact with the ocean. The waters of the North Atlantic
Ocean, which surround southern Greenland, are presently the warmest they have
been in the past 100 years. This warming is due to natural climate variability
and human induced climate change, and climate models project that it will keep
getting warmer. Therefore, it is important to understand if the present ocean
warming has contributed to ice loss from the Greenland Ice Sheet and how future
warming may result in even more ice loss.

The
paper describes the mechanisms causing the melting of the ice sheet,
particularly at its margin, where the glaciers extend into the ocean. This
so-called "submarine melting" has increased as the ocean and atmosphere have
warmed over the past two decades.

"What
a lot of research around Greenland and the fjords has shown is that if the
North Atlantic Ocean warms, then these warm waters will rapidly reach the
fjords and hence the margins of Greenland's glaciers," says Straneo.

But
scientists today know that the situation is more complex than just "a warmer
ocean melts ice."

A warmer
atmosphere is resulting in increased surface melting above the ice sheet, and
this runoff too enhances submarine melting. Surface melt water falls through
cracks in the glacier creating a freshwater river that rushes out into the
ocean at the base of the glacier, sometimes 600 meters (1,800 feet) below sea
level. This river mixes rapidly with the dense, salty seawater, contributing to
the heat transfer from the ocean to the ice, resulting in even more submarine
melting beneath the sea surface.